This definitely sounds like a bug with the Fitness app on the iPhone rather than anything else.
If we break it down..
1. Folks confirm the fitness data appears (you should be able to see this in the Health app) but the Fitness app doesn't display it.
2. The Fitness app _does_ display older workouts so it doesn't suggest that there's a change in format for the fitness data.
I'm wondering if it's just that the Fitness app is missing a trigger that there is new fitness data and maybe they changed that trigger with watchOS 7...?
What's the result of terminating the Fitness app and restarting it or, if that doesn't work, restarting the iPhone?
If we break it down..
1. Folks confirm the fitness data appears (you should be able to see this in the Health app) but the Fitness app doesn't display it.
2. The Fitness app _does_ display older workouts so it doesn't suggest that there's a change in format for the fitness data.
I'm wondering if it's just that the Fitness app is missing a trigger that there is new fitness data and maybe they changed that trigger with watchOS 7...?
What's the result of terminating the Fitness app and restarting it or, if that doesn't work, restarting the iPhone?